1. Field of the Invention
The present invention relates to a root apex position detection apparatus which is used to measure root canal length in dental diagnosis and treatment.
2. Description of the Related Art
When treating a tooth, a dentist sometimes needs to remove the dental pulp and nerve in the root canal. In this case, the dentist measures a distance between the tooth crown and the root apex and removes the dental pulp and nerve in the root canal by an amount corresponding to the distance or infected dentin or foreign bodies in the root canal. For distance measurement, a root apex position detection apparatus is used. In using the root apex position apparatus, a mouth electrode is placed in oral cavity, and a measurement electrode is inserted into the root canal. An AC signal is then applied between the measurement electrode and the mouth electrode, and the root apex position is detected in accordance with the value of a signal (electrical characteristic value) measured when the measurement electrode reaches the root apex position.
By monitoring that the indicator of a display unit indicates a predetermined position, the dentist knows that the measurement electrode has reached the root apex.
It is important for treatment in the root apex to accurately detect the root apex position of the tooth. If the root apex position is not accurately detected, the above distance will contain an error. If the dentist performs treatment trusting the distance containing the error, the dental pulp and nerve or infected dentin or foreign bodies may be left in the root canal, or the dentist may damage the root apex during operation.
The state inside the root canal of the tooth to be treated varies, case by case, from a dry state in which the interior of the root canal is dry to a wet state in which the interior of the root canal is filled with blood or the like. A conventional root canal length measurement apparatus can accurately detect the root apex position if the state inside the root canal of the tooth satisfies predetermined conditions (thickness, shape (arcuation or bifurcation), and the degree of dryness/wetness). If, however, the state inside the root canal of the tooth does not satisfy the specific conditions, the measured value contains an error.
A mark indicating the root apex position and marks adjacent to the root apex position are formed on a scale mark on the display of the conventional root apex position detection apparatus. If the state inside the root canal satisfies the specific conditions as described above, the scale mark can accurately indicate that the measurement electrode is located at the root apex position. However, the marks adjacent to the root apex position only indicate that the measurement electrode is located around the root apex position, but cannot indicate how far the measurement electrode is away from the root apex position.
In addition, before measuring the root canal length with a conventional root canal length measurement instrument, it is necessary to match a position of a silicone stopper inserted in a reamer or file to the root canal length by using a radiograph. Even if a mark is made by the silicone stopper added to the reamer or file or the silicone stopper added to the reamer or file which has once determined the root canal length, the silicone stopper is shifted, and an accurate length cannot be displayed in some cases. When the mark is hidden behind the tooth and cannot be recognized on a radiograph, the measurement operation must be stopped halfway.